This project concerns the maintenance and distribution of a cohesive and comprehensive database of information about restriction endonucleases and their associated methyltransferases. Key components of the database are information about the methyl sensitivity of restriction endonucleases and a comprehensive analysis of the restriction enzymes present in the sequenced microbial genomes. The performance site is New England Biolabs, located in Beverly, MA. REBASE has been in existence since 1975 and is currently implemented in a relational format in SYBASE. Information enters the database both from the published literature and by direct submission from the investigators either prior to publication or instead of publication. Approximately 10% of the entries describing experimental data are unpublished other than through REBASE. The information in REBASE is disseminated throughout the world both by formal publication in the scientific literature and in a variety of electronic formats. We post monthly updates and selected files are distributed through an automatic email list to more than 400 sites. In addition, the information is available by anonymous FTP or through the worldwide web. Among the files maintained and updated monthly, are specialized ones that are used by many of the more widely used computer programs such as GCG, McVector, DNA Strider, LaserGene, etc. These files are ready to use and include up-to-date information about the full range of restriction endonuclease specificities and their commercial availabilities. Information available through REBASE is key to all investigators planning experiments to cleave and/or religate DNA. It is a unique resource for the practice of biotechnology and its contents are used directly or indirectly by many sections of the research health care community.